Multicystic biliary hamartoma of the liver

A 59-year-old female patient, who was under follow-up for breast cancer, underwent an abdominal ultrasound, which revealed a multicystic hepatic lesion in the left lobe. The physical examination and laboratory findings were unremarkable.

Abdominal ultrasound revealed a cluster of small, anechoic tubular structures in the left hepatic lobe without internal vascularisation (Figures 1a and 1b).

A triphasic CT scan showed a subcapsular, lobulated, low-density lesion occupying nearly the entire left liver lobe (Figure 2a), predominantly comprising tubulocystic structures without common bile duct dilation (Figure 3). The lesion had smooth walls and internal thin septa with minimal enhancement (Figure 2b). No enhancing solid components or capsular retraction were noted, and the surrounding liver tissue appeared normal with no other focal lesions (Figure 3).

MRI showed a honeycomb-like lesion with high signal intensity on T2-weighted images (Figures 4a and 4b) and hypointensity on T1 (Figures 5a and 5b), without restricted diffusion (Figure 5c). MR cholangiopancreatography (MRCP) confirmed intrahepatic bile ducts’ cystic dilation (Figure 6).

Surgical exploration and immunohistochemistry confirmed the diagnosis of multicystic biliary hamartoma (Figures 7a, 7b and 7c).

Hepatic multicystic biliary hamartoma (MCBH) is a rare hepatic nodule, first identified in 2005, with fewer than twenty cases reported globally [1,2]. The origin of the lesion is uncertain but it is believed to result from ductal plate malformation [3,4]. MCBH may appear at any age and is usually asymptomatic, although some patients report abdominal pain. In rare cases, complications like infection, rupture, or biliary obstruction occur [3–5]. Due to its radiological similarity to other cystic liver lesions, preoperative diagnosis is challenging.

Radiologically, MCBH appears as a peripheral, multicystic lesion larger than 2 cm. Unlike Caroli disease or congenital hepatic fibrosis, MCBH lesions typically lack connection to the biliary tree and do not induce hepatic atrophy or hypertrophy [4,6–8]. Ultrasound reveals multiple small anechoic lesions with faintly hyperechoic septa, while CT shows subcapsular, water-density cystic formations with thin septa and minimal post-contrast septal enhancement [4–8]. On MRI, MCBH exhibits hypointensity on T1-weighted images and marked hyperintensity on T2-weighted images, with a honeycomb-like appearance [4–7].

Histologically, MCBH consists of hamartomatous cystic bile ducts, periductal glands, connective tissue, and normal hepatic parenchyma, with no malignancy indicators such as pleomorphism or atypia. Immunohistochemistry often reveals biliary-type keratin positivity (CK7 and CK19) in the cyst lining, aiding in diagnosis [9].

Differentiating MCBH from other cystic liver lesions is challenging. Caroli disease, for instance, arises from abnormal development of large intrahepatic bile ducts, sometimes accompanied by hepatic fibrosis. The “central dot sign” (an enhancing dot within dilated intrahepatic bile ducts) helps distinguish Caroli disease, which typically presents with saccular bile duct dilation and symptoms before the age of 30 [10]. The absence of a central dot sign, symptoms, or laboratory abnormalities in our 59-year-old patient made Caroli disease unlikely.

Other differential considerations include mucinous cystic neoplasms of the liver (MCN-L), which are typically larger and may contain septations or mural nodules [11]. Intraductal papillary neoplasms of the bile duct typically cause localised or diffuse biliary dilation through mucin secretion or mass effect. Imaging often reveals an intraductal, cauliflower-like papillary tumour that enhances during the late arterial phase [12]. Polycystic liver disease typically presents with hepatic and renal cysts [13].

Multicystic biliary hamartoma (MCBH) generally has a favourable prognosis, with no reported recurrences. Despite its benign nature, surgery is often performed due to nonspecific imaging features [1,9,14].

Written informed patient consent for publication has been obtained.